Farmer® Ionization Chamber 30012
Farmer chamber with graphite wall for reference dosimetry in high-energy photon, electron and proton beams
- Graphite wall
- Aluminum central electrode
- Sensitive volume 0.6 cm3 , vented
- Reference class in accordance with IEC 60731
The 30012 Farmer chamber is intended for reference dose measurements in radiation therapy.
Correction factors needed to determine absorbed dose to water or air kerma are published in the pertinent dosimetry protocols.
The graphite wall makes the chamber almost water equivalent, the aluminum central electrode improves the energy response at energies below 60Co.
The chamber is intended for the use in solid state phantoms and therefore not waterproof.
Specifications
| Type of product | vented cylindrical ionization chamber |
| Application | reference dosimetry in solid state |
| phantoms and air | |
| Measuring quantities | absorbed dose to water, air kerma, exposure |
| Reference radiation quality | 60Co |
| Design | not waterproof, vented, guarded |
| Direction of incidence | radial |
| Nominal sensitive volume | 0.6 cm3 |
| Nominal response | 20 nC/Gy |
| Long-term stability | ≤ 0.5 % per year |
| Chamber voltage | 400 V nominal |
| ± 500 V maximal | |
| Polarity effect at 60Co | < 0.5 % |
| Reference point | on chamber axis, 13 mm from chamber tip |
| Photon energy response | ≤ ± 2 % (70 kV ... 280 kV) |
| ≤ ± 4 % (200 kV ... 60Co) | |
| Directional response in solid state phantom | ≤ ± 0.5 % for rotation around the chamber axis and for tilting of the axis up to ± 5° |
| Leakage current | ≤ ± 4 fA |
| Cable leakage | ≤ 1 pC/(Gy·cm) |
Materials and measures
| Wall of sensitive volume | 0.425 mm graphite, 1.85 g/cm3 |
| Total wall area density | 79 mg/cm2 |
| Dimensions of sensitive volume | radius 3.05 mm |
| length 23.0 mm | |
| Central electrode | Al 99.98, diameter 1.15 mm |
| Build-up cap | PMMA, thickness 4.55 mm |
Ion collection efficiency at nominal voltage
| Ion collection time | 140 μs |
| Max. dose rate for | |
| ≥ 99.5 % saturation | 5 Gy/s |
| ≥ 99.0 % saturation | 10 Gy/s |
| Max. dose per pulse for | |
| ≥ 99.5 % saturation | 0.46 mGy |
| ≥ 99.0 % saturation | 0.91 mGy |
Ranges of use
| Chamber voltage | ± (100 ... 400) V |
| Radiation quality | 60 kV ... 50 MV photons |
| (10 ... 45) MeV electrons | |
| (50 ... 270) MeV protons | |
| Field size | (5 x 5) cm2 ... (40 x 40) cm2 |
| Temperature | (10 ... 40) °C |
| (50 ... 104) °F | |
| Humidity | (10 ... 80) %, max 20 g/m3 |
| Air pressure | (700 ... 1060) hPa |
Options
| T48012 | Radioactive check device 90Sr |
| T48002.3.003 | Chamber holding device for check device |